This invention relates to a two speed power tool. In particular the invention concerns a tool of this type comprising a housing, a rotation motor mounted in said housing, an output spindle, at least two planetary reduction gears located between said motor and said output spindle, the ring gear of a first planetary gear is rotatable relative to said housing as well as axially displaceable between a high speed position and a low speed position, and a coupling means associated with said housing and said first planetary ring gear to lock the latter against rotation either relative to the planet wheel carrier of said first planetary gear when occupying its high speed position or relative to said housing when occupying its low speed position.
A power tool of this type is previously described in U.S. Pat. No. 3,610,343. In this known tool shifting of a planetary gear ring gear between a low speed position and a high speed position is accomplished by a pneumatically actuated piston the operation of which is controlled by a valve system. This control valve system operates in response to the back pressure from the motor such that when the back pressure reaches a certain level pressure air is supplied to the pneumatic cylinder and the gear ring is shifted from its high speed position to its low speed position.
The main object of the present invention is to create an improved two-speed power tool in which the ring gear of a planetary gear is automatically shifted by a cam means from a high speed position to a low speed position and which does not involve any valve means for controlling the shifting of the ring gear.